This Junkers Jumo 004B Turbojet exhibit is
unique in that the Reidel 2 cycle starter motor is clearly visible. The Reidel
starter motor was started either electrically from the cockpit or by manually
using a lawn mower type pull cord with a ring that protrudes from the jet
engine nose cone. The Reidel starter motor was fueled by A3 80 octane gasoline
and 5% two stroke oil in a .8 gallon annular tank in the nose of the engine
nacelle.

Once the Reidel starter motor has started
the turbine is allowed to spin up to 800rpm. At this point the pilot presses 2
buttons, one to inject B4 (smelly synthetic brown coal fuel oil) and 3% oil
into the combustion chambers and another to light up the spark plugs to ignite
the fuel oil mixture. At 1,800rpm the starter button could be released
shutting off the starter motor allowing the turbine to spool up on its own. At
3,000rpm the ignition button for the glow plugs could be released and fuel
flow would be switched to straight B4 from the main fuel tanks. After this the
throttles could be advanced gradually to full power.

The Jumo 004 (109-004) Turbojet

The Jumo 004 project was initiated in late 1939 in a project led by Dr
Anselm Franz, then in charge of Junkers' turbo- and supercharger development.
The Heinkel company had proved the potential of jet propulsion as early as
1937, and the German Air Ministry encouraged other engine manufacturers to
initiate their own jet engine developments. The 004 was assigned the RLM
designation "109-004"

Click on Picture to enlarge

The Jumo 004 axial-flow Turbojet engine

German turbojet-engine development work had begun in the mid-1930s, with
the initial concepts conceived by an engineer named Hans-Joachim Pabst von
Ohain, whose efforts paralleled those of Frank Whittle of Britain.

In 1933, while von Ohain was working on his doctorate at the University
of Goettingen, he began investigate the gas turbine as a basis for an advanced
aircraft engine. Although most of the feedback he received suggested that gas
turbines would be too heavy for such a role, he pressed on anyway, developing
a demonstrator model of a "turbojet" engine in his garage, with the help of a
mechanic named Max Hahn.

Von Ohain managed to impress his professor, R.W. Pohl, with a test run
of the model. Pohl was both open-minded and well-connected, and in 1936 he
sent von Ohain on to aircraft manufacturer Ernst Heinkel with a letter of
recommendation. Von Ohain defended his ideas under grilling by Heinkel
engineers, and was put in charge of a design team to develop a practical
turbojet engine.

Von Ohain's team had a working bench-test prototype in September 1937,
six months after Whittle had reached the same benchmark. Von Ohain's prototype
burned hydrogen, which was not a practical fuel, but further work with Max
Hahn led to an engine that burned kerosene.

Ernst Heinkel gave the go-ahead to develop a flight-test engine,
designated the "HeS-3", which was strapped to an He-118 dive bomber for
evaluation. Tests began in May 1939 and continued until the engine burned
itself out a few months later. Enough had been learned to build a pure
jet-powered experimental aircraft, the "Heinkel He-178", powered by an
improved "HeS-3B" engine with 2.94 kN (300 kgp / 835 lbf) thrust. Later in the
flight test program, the He-178 would be fitted with a further improved
"HeS-6" turbojet with 5.78 kN (590 kgp / 1,300 lbf) thrust.

Click on Picture to enlarge

GVG/PD

The Heinkel He-178 was the first pure jet-powered aircraft

The He-178 was a simple "flying stovepipe", with straight-through
airflow from nose to tail. The aircraft had high-mounted tapered wings and a
conventional tail assembly. Although it had fully-retractable "tailsitter"
landing gear, the landing gear was bolted into the down position.

The He-178 performed its first test flight on 27 August 1939, a few days
before the outbreak of World War II. The flight lasted about five minutes,
with the pilot reporting that the aircraft "had no vibration and no torque
like a propeller engine. Everything was smooth, and ... felt wonderful." Von
Ohain was now well ahead of Whittle, whose efforts were bogged down, first by
official indifference and then by national crisis. Whittle would not fly his
own experimental jet aircraft, the "Gloster-Whittle G.40", until May 1941.

The Luftwaffe and the German Air Ministry ("ReichsLuftfahrtMinisterium /
RLM") were preoccupied with war, and the authorities didn't witness a flight
demonstration of the He-178 until November 1939. They were generally
unimpressed, since the He-178 was not as fast as the best piston fighters.
Heinkel was told: "Your turbojet is not needed. We will win the war on piston
engines."

After a total of about a dozen test flights, the He-178 was sent to the
national air museum in Berlin, where it was destroyed in a bombing raid in
1943. A second He-178 was planned, but not completed.

Although the RLM seemed indifferent to the He-178, the ministry was
nonetheless actively pushing German industry to develop turbojets. In
hindsight, it seems that the left and right hands of the RLM were not in
agreement, which summarizes most of the Third Reich's attempts to develop
advanced weapons.

Hans A. Mauch had become head of rocket development at the RLM in April
1938, and quickly expanded his office's charter to emphasize turbojet
development, working with an experimental department under Helmut Schelp in
the RLM research branch. By mid-1938, the two men had set up a comprehensive
program of jet engine development that was soon sponsoring a range of turbojet
and turboprop projects.

The design Dr Franz at Junkers Motoren (Jumo) initiated differed from
von Ohain's design by using a new type of compressor, recently developed by
the Aerodynamische Versuchsanstalt (AVA - Aerodynamic Research Institute) at
G�ttingen. This was an axial-flow compressor, which offered greater efficiency
and a smaller cross section then the earler designs.

In order to speed development and production of the new design, Dr Franz
used a simple combustion area using six "flame cans". This was less efficient
then the single annular can, but was simpler to implement. He also
collaborated on the development of the engine's turbine with Allgemeine
Elektricit�ts-Gesellschaft (AEG - General Electric Company) in Berlin. This
approach was proved correct when the Jumo 004 entered production and service
much earlier then the competing
BMW 003 design

Before this, in the fall of 1938, a Messerschmitt design team under Dr.
Waldermar Voight had drawn up concepts for a interceptor fighter with twin
turbojet engines. The preliminary designs for "Project 1065", as it was
designated, went through a iteration or two and finally resulted in a proposal
submitted to the RLM in May 1940

Messerschmitt's dream fighter had the turbojets mounted in nacelles
under the middle of the wings. The wings were slightly swept to ensure proper
center of gravity, and had an unusually thin chord, or ratio of thickness to
width, for good high-speed performance. Since the wing's features for
high-speed performance compromised low-speed handling, a "slat" was added to
the front of the outer wings. The slat was automatically extended to improve
handling at low speeds.

The fuselage had a triangular cross section and substantial fuel
capacity to feed the thirsty engines. The aircraft was a "taildragger", with
fully retractable landing gear. In July 1940, the RLM ordered three
prototypes, under the designation "Messerschmitt 262 (Me-262)", to be powered
by BMW-003 engines.

Airframe development far outpaced engine development, and so the first
prototype, the "Me-262-V1" ("V" standing for "Versuchs / Experimental"), was
fitted with a single Jumo-210G piston engine with 530 kW (710 HP) and a
two-bladed propeller for preliminary test flights. First flight was on 18
April 1941. The RLM was becoming more interested in the aircraft, ordering
five more prototypes in July 1941, to follow the initial order for three.

The Me-262-V1 was finally fitted with a pair of BMW-003 turbojets, each
with 5.40 kN (550 kgp / 1,200 lbf) thrust, in November 1941. The Jumo 210G
piston engine was retained, which was fortunate, since the turbojet engines
were hopelessly unreliable. On 25 March 1942, Messerschmitt test pilot Fritz
Wendel took off and suffered immediate failures of both engines. He managed to
make a go-round on the piston engine and land, damaging the aircraft but
suffering no injury himself.

The
BMW 003 engine was abandoned for the Me 262, being replaced by the Junkers
Jumo-004 which seemed more promising. The third prototype, the "Me-262-V3",
was fitted with two Jumo-004A pre-production engines with 8.24 kN (840 kgp /
1,850 lbf) thrust each. Wendel took the V3 into the air on 18 July 1942 and
found the aircraft extremely impressive. Work on the
BMW 003 continued at BMW, and by late 1942 it had been made far more
powerful and reliable. The improved engine was flight tested under a Junkers
Ju 88 in October 1943 and was finally ready for mass production in August
1944.

Apart from the Me 262 and Arado Ar 234, the engine was used to power the
experimental Junkers
Ju 287 , and prototypes of the Gotha Go 229 and Heinkel He 280. There were
plans to install it in the Heinkel He 162 as well as the Focke-Wulf Ta 183 and
Henschel Hs 132 then under development.

Following World War II, Jumo 004s were built in small numbers by
Malesice in Czechoslovakia, designated M-04 to power the Avia S-92, itself a
copy of the Me 262. Jumo 004 copies were also built in the Soviet Union as the
RD-10 engine, where they powered the Yakovlev Yak-15 as well as many prototype
jet fighters.

In France, captured 004s powered the Sud-Ouest SO 6000 Triton and the
Arsenal VG-70.

Derived from an article by Greg Goebel

Junkers Jumo 004

Jumo 004

Cutaway example of a Junkers Jumo 004 jet engine at the National Museum
of the U.S. Air Force, Wright-Patterson AFB, Ohio.

Design and development

The practicality of jet propulsion had been demonstrated in
Germany in early 1937 by Hans von Ohain working with the
Heinkel company.Most of the
RLM remained uninterested, but Helmut Schelp and Hans Mauch saw the
potential of the concept and encouraged Germany's aero engine manufacturers
to begin their own programmes of jet engine development.The companies remained skeptical and little new development
was carried out.Eventually in 1939 Otto Mader, head of
Junkers Motoren (Jumo), stated that even if the concept was useful, he had
no one to work on it.Schelp responded by stating that
Dr Anselm Franz, then in charge of Junkers' turbo- and supercharger development, would be perfect for the job.Franz started his development team later that year, and the
project was given the RLM designation 109-004 (the 109- prefix was
common to all jet projects).

Franz opted for a design that was at once conservative and
revolutionary.His design differed from von Ohain's in
that he utilised a new type of compressor which allowed a continuous, straight flow of air through the
engine (an axial compressor), recently developed by the
Aerodynamische Versuchsanstalt (AVA - Aerodynamic Research
Institute) at
Göttingen.The axial-flow compressor not only had
excellent performance, about 78% efficient in "real world" conditions, but
it also had a smaller cross-section, important for a high-speed aircraft
design.

On the other hand, he aimed to produce an engine that was
far below its theoretical potential, in the interests of expediting
development and simplifying production.One major
decision was to opt for a simple combustion area using six "flamecans", instead of the more efficient single
annular can.For the same reasons, he collaborated
heavily on the development of the engine's turbine with
Allgemeine Elektrizitäts-Gesellschaft (AEG - General Electric
Company) in berlin, and instead of building development engines, opted to begin work
immediately on the prototype of an engine that could be put straight into
production.Franz's conservative approach came under
question from the RLM, but was vindicated when even given the developmental
problems that it was to face, the 004 entered production and service well
ahead of its more technologically advanced competitor, the
BMW 003.

Technical description and
testing

Frontal view of a Jumo 004 engine mounted in a
nacelle on an Me 262 fighter.The pull-starter
handle is clearly visible in the center of the engine.

The first prototype 004A, which was constructed to
run on Diesel fuel, was first tested in October 1940, though without an exhaust
nozzle.It was bench tested at the end of January 1941
to a top thrust of 430 kgf (4,200 N; 950 lbf), and work continued to
increase the output, the RLM contract having set a minimum of 600 kgf (5,900
N; 1,300 lbf) thrust.[1]

Vibration problems with the compressor blades delayed the
program at this point, until a new stator design by Max Bentele solved the
problem. The original alloy compressor blades were replaced
with steel ones and with the new stators in place the engine developed 5.9
kN in August, and passed a 10-hour endurance run at 9.8 kN in December.The first flight test took place on March 15 1942, when a
004A was carried aloft by a
Messerschmitt Bf 110 to run up the engine in flight.

On July 18, one of the prototype
Messerschmitt Me 262s flew for the first time under jet power from its
004 engines, and the 004 was ordered into production by the RLM to the
extent of 80 engines.

The initial 004A engines built to power the Me 262
prototypes had been built without restrictions on materials, and they used
scarce raw materials such as nickel, cobalt, and molybdenum in quantities which were unacceptable in production.Franz realized that the Jumo 004 would have to be redesigned
to incorporate a minimum of these strategic materials, and this was
accomplished.All the hot metal parts - including the
combustion chamber - were changed to mild steel protected by an aluminum coating, and the hollow turbine
blades were produced from folded and welded Cromadur alloy (12% chromium,
18% manganese, and 70% iron) developed by krupp, and cooled by compressed air "bled" from the compressor.The engine's operational lifespan was shortened, but on the
plus side it became easier to construct.[1]

The first production model of the 004B weighed 220
lb (100 kg) less than the 004A, and in 1943 had passed several 100 hour
tests, with a time between overhauls of 50 hours being achieved.[2]

Later in 1943 a series of engines suffered vibration
problems, and solutions dragged on.Eventually, in
December, blade-vibration specialist Max Bentele was once again brought in during a meeting at the RLM
headquarters, and the problem was solved by raising the blades' natural
frequency by increasing their taper, shortening them by 1 millimeter, and
reducing the operating speed of the engine from 9,000 to 8,700 rpm.

It was not until early 1944 that full production could
finally begin.These setbacks were the principal
factor delaying the Luftwaffe's introduction of the Me 262 into squadron
service.

Given the lower-quality steels used in the 004B, these
engines typically only had a service life of some 10-25 hours, perhaps twice
this in the hands of a skilled pilot.Another
shortcoming of the engine, common to all early turbojets, was its sluggish
throttle response.Worse, it was fairly easy to inject
too much fuel into the engine by throttling up too quickly, allowing heat to
build up before the cooling air could remove it.This
led to softening of the turbine blades, and was a major cause for engine
failures.Nevertheless, it made jet power for combat
aircraft a reality for the first time.

Riedel starter

The exhaust area of the 004 featured a variable geometry
nozzle, which had a special restrictive body nicknamed the Zwiebel
(German for onion, due to its shape when seen from the side) which had
roughly 40 cm (16 inch) fore-and-aft travel to vary the jet exhaust's
cross-sectional area for thrust control, as the active part of a pioneering
"divergent-convergent" nozzle format.

One interesting feature of the 004 was the starter system,
which consisted of a Riedel 10 hp (7 kW) 2-stroke motorcycle engine hidden in the intake.A hole in
the extreme nose of the centrebody contained a pull-handle which started the
piston engine, which in turn spun up the turbine.Two
small gasoline tanks were fitted in the annular intake.

The Jumo 004 could run on three types of fuel:[3]

J-2, its standard fuel, a
synthetic fuel produced from coal.

Diesel oil.

Aviation gasoline; not considered desirable due to its
high rate of consumption.

Postwar production

Following World War II, Jumo 004s were built in small
numbers by
Malešice in
Czechoslovakia, designated M-04, to power the
Avia S-92 which was itself a copy of the Me 262.
Jumo 004 copies were also built in the
Soviet Union as the
RD-10 engine, where they powered the
Yakovlev Yak-15 as well as many prototype jet fighters.

In
France, captured 004s powered the
Sud-Ouest SO 6000 Triton and the
Arsenal VG-70.

Variants

A number of more advanced versions were in development at
the end of the war.The 004C included an
afterburner for increased thrust, but was not built.The 004D improved fuel efficiency with a two-stage
fuel injector, and introduced a new throttle control that avoided dumping
too much fuel into the engine during throttle-ups.The
004D had passed testing and was ready to enter production in place of the
004B, when the war ended.The 004E was a 004D
model with an improved exhaust area for better altitude performance.

A much more advanced model based on the same basic systems
was also under development as the Jumo 012.The
012 was based on a "two-spool" system, in which two turbines, spinning at
different speeds, drove two separate sections of the compressor for more
efficiency.In a jet engine the compressor typically
uses up about 60% of all the power generated, so any improvements can have a
dramatic effect on fuel use.Plans were also underway
to use the 012's basic concept in an engine outwardly identical to the 004,
known as the 004H, which improved
specific fuel consumption from the 004B's 1.39 kg/(daN*h) to a
respectable 1.20 kg/(daN*h), a decrease of about 15%.

Applications

Apart from the Me 262 and
Arado Ar 234, the engine was used to power the experimental
Junkers Ju 287, and prototypes of the
Horten Ho 229 and
Heinkel He 280.There were plans to install it in
the
Heinkel He 162 as well as the
Focke-Wulf Ta 183 and Henschel Hs 132 then under development.